(1) Field of the Invention
This invention relates to magnetic shielding of a magnetic sensing device and more particularly to a magnetic shield using a layer of single domain ferromagnetic material, formed on a layer of antiferromagnetic exchange material to stabilize the single domain nature of the ferromagnetic material, as a key part of the shield.
(2) Description of the Related Art
One of the major challenges of magnetic recording and sensing devices, such as those devices using spin valve, anisotropic magnetoresistive, spin dependent tunneling magnetic sensor devices is the amplitude stability of the sense current after write excitation. The strong field used for write excitation can rearrange the domain patterns of the shields shielding the magnetic sensor device. After the writing cycle has been completed the domains in the shield will relax to their final domain state, Since these shields are magnetically coupled to the magnetic sensor device, this relaxation of the domains to the final domain state will cause noise, such as pop-corn noise and covariance of amplitude noise, in the sense current.
U.S. Pat. No. 5,898,548 to Dill et al. describes a magnetic recording system with a magnetic tunnel junction magnetoresistive read head located between two spaced-apart magnetic shields. Electrically conductive spacer layers are located at the top and bottom of the magnetic tunnel junction device and connect the magnetic tunnel junction device to the shields.
U.S. Pat. No. 5,828,530 to Gill et al. describe a spin valve sensor device wherein the spin valve sensor is asymmetrically located between first and second shield layers so that image currents from the first and second shield layers partially or completely counterbalances a stiffening field from antiferromagnetic, pinned, and spacer layers.
U.S. Pat. No. 5,883,763 to Yuan et al. describes a read/write head having a giant magnetoresistive sensor biased by permanent magnets located between the giant magnetoresistive element and the pole shields.
In most magnetic recording and sensing devices the sensing device and writing device are packaged in the same recording/sensing head. This close proximity of the sensing and writing device, along with other reasons, requires the use of magnetic shields around the magnetic sensing device. A conventional shielding arrangement is shown schematically in FIGS. 1 and 2. FIG. 1 shows a magnetic sensing device 18 disposed between a first magnetic shielding element 14 and a second magnetic shielding element, wherein both the first and second magnetic shielding elements are ferromagnetic material. A magnetic writing device 20, such as an inductive coil, is shown between the second magnetic shielding element 16, which typically also functions as a first pole piece for the writing means and a second pole piece 17 for the writing means. The magnetic sensing device 18 and the ends of the pole pieces are located a first distance 12 from the magnetic recording media 10, such as a magnetic disk.
FIG. 2 shows a view of the magnetic recording and sensing device looking out of and perpendicular to the magnetic recording media 10 of FIG. 1. The view of FIG. 2 is a taken perpendicular to the view shown in FIG. 1. FIG. 2 shows the magnetic sensing device 18 between the conventional first magnetic shielding element 14 and conventional second magnetic shielding element 16. The conventional second magnetic shielding element 16 is shown between the magnetic sensing unit 18 and the second pole piece 17.
One of the problems encountered in the conventional shielding arrangement is that the strong magnetic fields used for writing data into the magnetic media can rearrange the domain patterns of the first shielding element 14 and the second shielding element 16 used to shield the magnetic sensing device 18. After the writing cycle has been completed the domains in the first and second shield elements will relax to their final domain state. Since these shields are magnetically coupled to the magnetic sensor device 18, this relaxation of the domains to the final domain state will cause magnetic field fluctuations at the magnetic sensor device 18.
The magnetic sensing device 18 comprises sensing elements such as a spin valve, anisotropic magnetoresistive, spin dependent tunneling magnetic sensing head or other giant magnetoresistive magnetic sensing head which are sensitive to the magnetic field fluctuations. These magnetic field fluctuations caused by the relaxing of the domains to their final state in the first and second shield elements will cause noise, such as pop-corn noise and covariance of amplitude noise, in the sense signal from the magnetic sensing device and complicate the process of reading the data stored in the magnetic media.
It is a principle objective of this invention to provide a magnetic shielding element which will not cause noise in the sensing signal of a magnetoresistive sensing device because of domains in the shielding material relaxing to their final state.
It is another principle objective of this invention to provide a magnetic recording and sensing device which will not have noise in the sensing signal of a magnetoresistive sensing device because of domains in the material used to shield the magnetic sensing device relaxing to their final state.
These objectives are achieved by forming new shielding elements. These shielding elements have a layer of antiferromagnetic exchange material formed on a layer of first ferromagnetic material. The first ferromagnetic material is stabilized by the antiferromagnetic exchange material to form a single domain state. A layer of non-magnetic metal is then formed on the layer of antiferromagnetic exchange material. A layer of second ferromagnetic material is then formed on the layer of non-magnetic metal to complete the shield element. The shield element is also the first pole piece of the magnetic writing means.
The magnetic fields used during the writing cycle will disturb both the domains in the layer of single domain first ferromagnetic material and the layer of second ferromagnetic material. However, the domains in the single domain first ferromagnetic material will relax to its single domain state with a relaxation time of pico seconds so that the single domain first ferromagnetic material will be completely relaxed to its single domain state before any data is read by the magnetic sensing device. The magnetic shielding elements are arranged so that the magnetic sensing device is between two magnetic shielding elements wherein the layer of single domain first ferromagnetic material of each shielding element is adjacent to the magnetic sensing device. The layer of single domain first ferromagnetic material of each shielding element shields the magnetic sensing device from the slower relaxation of the domains of the second ferromagnetic layer in each of the shielding elements. This arrangement shields the magnetic sensing device from magnetic field fluctuations and the problems of pop-corn noise and covariance of amplitude noise during readback of data from the disk are avoided.